The use of natural and synthetic materials for bone repair is known. Most of the synthetic materials share numerous advantages over natural materials (including allograft bone, autograft bone and demineralized bone matrix (“DBM”)) such as unlimited supply, elimination of disease transmission, elimination of second surgery, and the ability to be shaped into various shapes and sizes. Many synthetic bone grafts include materials that closely mimic mammalian bone, such as compositions containing calcium phosphates. Exemplary calcium phosphate compositions contain type-B carbonated hydroxyapatite [Ca5(PO4)3x(CO3)x(OH)], which is the principal mineral phase found in the mammalian body. The ultimate composition, crystal size, morphology, and structure of the body portions formed from the hydroxyapatite are determined by variations in the protein and organic content. Calcium phosphate ceramics have been fabricated and implanted in mammals in various forms including, but not limited to, shaped bodies and cements. Different stoichiometric compositions such as hydroxyapatite (“HAp”), tricalcium phosphate (“TCP”), tetracalcium phosphate (“TTCP”), and other calcium phosphate salts and minerals, have all been employed to match the adaptability, biocompatibility, structure, and strength of natural bone. The role of pore size and porosity in promoting revascularization, healing, and remodeling of bone has been recognized as a critical property for bone grafting materials. The preparation of exemplary porous calcium phosphate materials that closely resemble bone have been disclosed, for instance, in U.S. Pat. Nos. 6,383,519; 6,521,246 and 6,991,803 incorporated herein by reference in their entirety.
Recently, in an attempt to broaden the use of bone graft materials throughout the body, pliable and injectable bone graft compositions have been fabricated. Some of these attempts have been disclosed in U.S. Pat. No. 5,324,519 to Dunn, et al.; U.S. Pat. No. 5,352,715 to Wallace et al.; U.S. Pat. No. 6,287,341 to Lee et al.; U.S. Pat. No. 6,214,368 to Lee et al.; U.S. Pat. No. 6,652,887 to Richelsoph et al.; and U.S. Pat. No. 6,288,043 to Spiro et al. However, these attempts suffer from numerous shortcomings. Some compositions are made of thermoplastic polymers as opposed to calcium phosphate. There are injectable implant compositions that teach having ceramic:collagen ratios requiring a collagen dominance. There are also compositions used as implants made of poorly crystalline apatitic calcium phosphate defined by a specific XRD spectrum and FTIR pattern. Other attempts have focused on compositions made from calcium sulfate.
Furthermore, many of these bone attempts include materials that do not optimally resorb (e.g., thermoplastic polymers, amorphous calcium phosphate, calcium sulfate dihydrate) or structures that do not have the ideal porosity and pore size distribution to promote bone formation. Other attempts require the addition of a carrier, such as hyaluronic acid or glycerol, or a plasticizer in a high percentage so that the compositions may be shaped or injected. Several also require that the mineral component particle size be smaller than 250 μm to facilitate injection.
In addition, because the flowability and wash-out resistant properties have an inverse relationship, there exists a problem that if the flowability/injectability of the bone graft material increases, the wash-out resistant property thereof decreases.
Therefore, there is a need for injectable, resorbable bone graft materials with improved handling properties that maintain physical integrity in a wet environment, such as in the presence of body fluids at a defect site.
There is also a need for resorbable, porous, injectable bone graft materials that maintain ideal osteoconductivity properties, offer convenient delivery for a variety of applications and can occupy voids of varying shapes for restoring defects in bone.